The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out. Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes.There's a small amount of radioactive carbon-14 in all living organisms.When they die no new carbon-14 is taken in by the dead organism.
Scientists find out the age of a dinosaur fossil by dating not only the rocks in which it lies, but those below and above it.
The carbon-14 it contained at the time of death decays over a long period of time.
By measuring the amount of carbon-14 left in dead organic material the approximate time since it died can be worked out.
Fossils are the remains of animals or plants that lived a long time ago.
When we think of fossils, the first things that come to mind are the bones of dinosaurs; but a fossil can be anything.